1. Field of the Invention
The present invention relates to a transmission system having an auxiliary transmission for use in two- or three-wheeled motorcycles. The invention also relates to a transmission system having main and auxiliary transmissions, wherein transmission operations for both the main and auxiliary transmissions are performed by the same power shift mechanism.
2. Background Art
As a conventional transmission system for motor bicycles, motor tricycles, or the like, a transmission system is most generally used in which two rows of shafts for mounting multi-stage gears are disposed in parallel to each other to thereby cause mutually facing gears to normally engage with each other. In the this system, the rotation of an engine power shaft is transmitted to the drive wheels such as the vehicle rear wheels by the suitable selection of combinations of gears to change or maintain the speed.
Generally, the tansmission system for very efficiently utilizing the motive power characteristics of the engine in accordance with the running conditions of the engine. Accordingly, as the demand for higher performance motorcycles becomes stronger, a trend exists to further improve the running performance by changing the speed in smaller steps and by increasing the number of available gear ratios. To satisfy this trend, high performance transmissions have increased the number of gears by using multiple stages of gearing or an auxiliary transmission is serially connected to the conventional transmission system, which is then regarded as the main transmission.
Problems occur in both of these cases. In the former case, the problem is that the width of the transmission system becomes large because of the increase in gears (the gear shafts are arranged transversely) and the addition of incidental shifting equipment. In measuring running performance, the bank angle is one of the important factors for motorcycles. This bank angle is the maximum angle at which the cycle can be inclined. The larger the bank angle, the more the center of gravity in the cycle body can be lowered and the more the turning performance can be improved, so that handling becomes more comfortable. However, the transmission system is generally disposed in the vicinity of the bottom of the cycle body, and therefore in order to make the bank angle large it is necessary to reduce the width of the transmission system as much as possible. It is difficult however to reduce the width of the conventional multi-stage gearing type transmission system, because many gears must be disposed in the transverse direction. Consequently, the more the number of gears per shaft increases, the more difficult it becomes to secure the necessary bank angle. Furthermore, as the number of gear stages increases, the weight of the cycle body increases, resulting in a reduction in measure of running performance such as acceleration, fuel efficiency, etc., as well as an increase in cost.
In the latter case, i.e., in the case of the additional provision of an auxiliary transmission, it is necessary to connect at least one new gear mounting shaft in parallel to the conventional main transmission. Accordingly, the overall size of the transmission system composed of the main and auxiliary transmissions becomes large in the lengthwise direction. Consequently, the weight increases because of the enlarged size of the transmission system. Thus, this system is disadvantageous in view of cycle body layout, running performance, cost, etc.
In the case where an auxiliary transmission was additionally provided, individual operation members were provided respectively in the main and auxiliary transmissions, and were actuated independently of each other. For example, the speed change operations of the main and auxiliary transmissions were performed with the foot and the hand respectively.
Moreover, in the prior art, if the main and auxiliary transmissions both include separate speed change operation members and the operation members are actuated independently of each other, the independent actuations require independent use of the foot and hand, which is difficult for the driver. In addition, it is almost impossible to select and determine the respective speed change positions for the main and auxiliary transmissions which provide the optimum combination. Accordingly, sometimes, the capability of the auxiliary transmission cannot be sufficiently utilized.